This relates generally to imaging systems and, more particularly, to imaging systems having circuitry for handling the eclipse phenomenon.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Column circuitry is coupled to each pixel column for reading out pixel signals from the image pixels. The column circuitry often implements a correlated double sampling (CDS) process, which involves obtaining pixel signals by computing the difference between reset signals sampled during reset operations and image signals sampled following charge transfer operations.
The eclipse phenomenon occurs when at least some pixels are exposed to strong light such as direct illumination from the sun. The strong light may cause the floating diffusion to leak, which results in an erroneous reset signal being sampled (i.e., reset signals sampled during reset operations may exhibit voltage levels that are less than the desired reset level). Consequently, the pixel signal computed via CDS becomes a smaller value, the effect of which is manifested when an over-illuminated pixel appears dark when it should be bright.
It is within this context that the embodiments herein arise.